1. Field of Use
This invention relates to mechanically joining a hollow composite tube of filamentary material that is composed of glass, graphite, aramid, boron or other such filaments and a polymer matrix to a metallic end connection fitting or to other tubes which are of same or like configurations. The invention has application where it is desirable to transfer torsional, bending and axial forces to an external or internal structural part from a composite tube containing the joined end fitting such as in a rocket motor casing, a fluid conveyance pipe, a pressurized fluid containment vessel, a torque transmitting shaft, and a load transmitting structural strut all of which employ a composite tube.
2. Prior Art
In the field of metal-to-composite joints, the connection of the metal fitting or the external structure to the filamentary composite tube has not been made in a manner as to take full advantage of the multiplicity of load transfer planes within the tube. Such cases of prior art are those where the fitting or external structure is bonded together with the composite tube through a singular plane being either internal or external to the fitting and where the singular plane is either uniform as a cylinder or non-uniform as a spline, knurled or otherwise interrupted for the purpose of increasing penetration of the fitting surface into the composite tube material. The present invention takes full advantage of multiplicity of load transfer planes occurring between each layer of the composite tube by having intermediate shells of material located at each plane all of which carry the load to a second point of transfer.
In other cases of prior art in metal-to-composite joints, connections have been made by radially pinning or bolting through the composite tube into the fitting In this manner, the load is transferred through bearing stresses in the composite tube layers which have limited and very low bearing strength compared with that of metal. The present invention incorporates metal shells by which the load is in turn transferred through a continuous fusion weld to the fitting or adjacent structure or by a much greater bearing strength of the metal shells thru pins, bolts or rivets.
In still other cases of prior art, metal shims have been used to axially reinforce the regions locally around bolt holes. In this manner, circumferential loads and torsional shear loads cannot be transferred from the composite layers to the bolts. The present invention uses metal shells extending around, between and beyond fasteners which efficiently transfer torsional shear and axial loads and carry circumferential loads in the entire embedded zone.